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<H1>Rules for Penalty calculation</H1>There are two sorts of transformation: (a) conversion from one format
into another, for reasons of presentation, and whereby information
generally is lost, and (b) encoding, for reasons of speed (compaction),
security (encryption), or transmission, and whereby the information
and format remain untouched.<P>
There are two questions to consider when deciding on different possible
transfer formats between servers and clients: Information degradation
and elapsed time. 
<H2>Degradation</H2>When information is converted from one format to another,  it may
be degraded. For example, when a postscript file is rendered into
bitmap, it loses its potentially infinite resolution; when a TeX file
is rendered into pure ASCII, it loses its structure and formatting.<P>
This degradation is difficult to guess from simply the file type.
and for a given file it is quite subjective. Any attempt to estimate
a penalty will therefore be very aproximate, and only useful for distinguishing
widely differing cases. A suitable unit would be the proportion, between
0 and 1, of the information which is not lost. Let's call it the degradation
coefficient.  One would hope that these coefficiemnts are multiplicative,
that is that the process of converting a document into one format
with degradation coeficient c1 and then further converting the result
of that with coeficient c2 would in all be a process with coeffcient
c1*c2.  This is not, in fact, necessarily the case in practice but
is a reasonable guess when we know no better. 
<H2>Elapsed time</H2>The elapsed time is another penalty of conversion. As an aproximation
one might assume this to be linear in the size of the file.  It is
not easy to say whether the constant part or the size-proportional
part is going to be the most important. The server, of course, knows
the size of the file.  It can in fact as a result of experience make
improving guesses as to the conversion time. The conversion time will
be a function also of local load.  For particular files, it may be
affected by the caching of final or intermediate steps in a conversion
process. Given a model in which the server makes the decision on the
basis of information supplied by the client,  this information could
include, for each type,  both the constant part (seconds) and the
size-related part (seconds per byte).<P>
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<ADDRESS><A NAME=0 HREF=../../TBL_Disclaimer.html>Tim BL, RC</A></A>
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